1. Field of the Invention
This invention relates to a lead frame transporting device and more particularly to a device that detects top/bottom/front/back orientations of a lead frame that is fed into a die bonder, wire bonder, etc., thus preventing bonding errors.
2. Prior Art
Generally, in die bonding, lead frames stored in a lead frame loader are pushed out of the loader one at a time by a pusher onto feeder rails. On the feeder rails, a lead frame is pitch-fed to a preform station and then to a bonding station.
More specifically, on the preform station, adhesive is drip-applied to the lead frame by preform assembly, then on the following bonding station a bonding head performs the die bonding to the lead frame. The position of the lead frame on the preform and bonding stations is set by inserting positioning pins in holes that are opened near both side edges of the lead frames.
However, the operator sometimes makes a mistake when storing the lead frames in the loader. For instance, the direction or orientation of the lead frames are not consistent in the loader. In prior art devices, detection of improper top/bottom/front/back orientation of a lead frame that is derived from the erroneous storing of the lead frames in the loader is performed by detecting whether or not a positioning pin provided at the preform station is entered a specific lead frame hole. An example of this type of device is disclosed in the Japanese Utility Model Application Publication (Kokoku) No. 57-29310.
In this prior art, however, errors in top/bottom/front/back orientation of the lead frame are not able to be detected until the lead frame is fed to the preform station. This is a problem, because for the lead frame that is improperly oriented on the preform station, correction of such an improper orientation cannot be easily done. Also, if the positioning holes of the lead frame are positioned symmetrically with respect to the direction in which the lead frame is transferred, the pin would enter the positioning holes even if the lead frame orientation is reversed, resulting in the improper orientation of the lead frame not being detected.